Previous data relating to the cost of water fluoridation have frequently been limited to variable costs such as chemicals and other materials. The purpose of this study was to measure opportunity costs and to estimate a cost curve for water fluoridation. Data were collected from 44 Florida communities which had initiated community water fluoridation between 1981 and 1989. Equipment installation and engineering costs were derived from actual invoices and adjusted to 1988 dollars. Output of the water systems was measured by water usage and community population. For large systems, average costs approached an asymptote at $0.21 per person per year when population was used as a measure of output and $1,199 per year to fluoridate one million gallons of water daily. Most of the economies of scale were exhausted with water systems serving moderate sized towns with 10,000 to 50,000 people. While water usage is conceptually the preferred output measure, results indicate that population can serve as a very good proxy when water usage is not available. L shaped average cost curves were very good models of fluoridation. Long range average cost curves exhibited economies of scale. Economic considerations which implied nonlinear constraints on the model parameters were analyzed. These constraints are nearly satisfied by the linear model and had a very small effect on the parameter estimates.